I am curious how much a rewrite staying in Ruby could have saved. Its always easier to write code when you have a good specification, and a working application would fulfill that role well.
That would mean something if Ruby apps are 100% Ruby and/or are performing binary tree operations all the time, or doing similar kinds of CPU-intensive operations as depicted in the alioth benchmarks. But they don't. Ruby web apps perform lots of string manipulation, memory allocation, I/O. A lot of expensive things are offloaded to C libraries. Things like XML parsing are offloaded to native libraries like libxml; nobody uses an XML parser fully implemented in Ruby. Ruby does not reimplemented gzip compression in Ruby, it uses zlib. So the alioth benchmarks are not representative of real-world performance.
That benchmark performs string manipulations that rarely occur in web apps. Web apps need: concatenation, substring, find/replace, maybe with regexps. All of those are implemented in C.
> memory allocation
Web apps don't tend to implement entire trees in pure Ruby. That benchmark is completely non-representative of real-world performance.
What exactly are you getting at? Of course it's easy to find a bunch of synthetic benchmarks that show weaknesses in particular cases. Still doesn't prove anything.
Order of magnitude faster? I doubt that. Unless the old ones were really old / slow to begin with. But really, we are both speculating without knowing the facts.
It's very difficult to do a comparison like this in practice, because switching languages inherently involves a rewrite of a platform.